Active Volcano Mt. Kusatsu-ShiraneActive Volcano Mt. Kusatsu-Shirane

Rain

Mt. Kusatsu-Shirane, an active volcano, is a mountain of sulfur. At its summit, which is barren of almost all plant life, is an emerald green crater lake. Rainwater seeps into the mountain through the lake and wells up from around its base as highly acidic water to form rivers and hot springs.

Mt. Kusatsu-Shirane’s Blessing: Kusatsu OnsenMt. Kusatsu-Shirane’s Blessing: Kusatsu Onsen

Kusatsu Onsen, one of Japan’s major acidic hot springs, boasts the highest natural output of any hot spring in the country: more than 32,300 liters per minute or 230,000 barrels per day.With a strong acidity of pH 2.0, Kusatsu Onsen’s water is uniquely antibacte-rial and possesses multiple efficacies that have healed the bodies and souls of many over the centuries.

“Rivers of Death” Near Kusatsu“Rivers of Death” Near Kusatsu

While the acidic waters of Kusatsu Onsen possess the efficacies of a hot spring, they also have a harmful effect on people’s lives. The rivers issuing from Mt. Kusatsu-Shirane and the surrounding area have been a source of anxiety over the years for those living in the region due to their high acidity. In addition to the rivers’ natural acidity, acidic wastewater flowed into them from local mines that gathered sulfur for use in such things as gunpowder. The extremely acidic waters of these small and medium rivers then flowed into the Agat-suma River, making it unusable by people in their daily lives and unsuitable for other living things. As a result, those living near the rivers came to call them “rivers of death.”

A Neutralization ProjectSafeguarding People’s Lives

“Yubatake,” the symbol of Kusatsu Onsen

Yubatake

(Hot Water Fi

eld)

YukawaRiver

A nail immersed in the acidic waterof the Yukawa River over 15 days

Original

Originalconcrete 3 days 1 week 2 weeks 1 month

Acidic river

Day 1Day 2

Day 3Day 4

Day 5Day 6

Day 7Day 8

Day 9Day 10

Day 12Day 15

Concrete immersed in the acidic waterof the Yukawa River over a month

pH2.0pH2.0

The Yukawa R i ve r, where the waters of Kusatsu Onsen flow. The river maintains a temperature of nearly 30℃ even in winter.

Sulfur

Shinaki Dam Water Quality Management OfficeKanto Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism604-1 Kusatsu, Kusatsu-machi, Agatsuma-gun, Gunma 377-1711 TEL 81-279-88-5677／URL http://www.ktr.milt.go.jp/sinaki

Mt. Shirane

Shinaki DamWater Quality

Management Office

NeutralizationPlant

of Kakusa

NeutralizationPlant

of Kusatsu

Yukawa River

SuzuranMonitoringStation

Yazawa RiverMonitoringStation

Yazawa River

Osawa River

Osawa RiverMonitoring Station

DamControlStation

YukawaPowerStation

Shinaki Dam

ShirasunaRiver

Shinaki Area of the former Kuni Village

The Neutralization Project That Revived the Rivers of DeathThe Neutralization Project That Revived the Rivers of Death

The neutralization project being carried out at the Neutralization Plant of Kusatsu was started in 1964, the first of its kind in the world. Its goal was to improve the water quality of the acidic rivers flowing into the Agatsuma River. The project introduces limestone powder into the Yukawa, Osawa and Yazawa Rivers, and the result-

ing neutralized waters then flow into the Agat-suma River by way of the Shirasuna River.

Shinaki Dam: Accumulating the Neutralization ProductShinaki Dam: Accumulating the Neutralization Product

The introduction of limestone powder into the Yukawa, Osawa and Yazawa Rivers by the Neutralization Facili-ties creates a neutralization product that the Shinaki Dam was built to accumulate. The dam was completed in 1965 with the cooperation of the residents of the Shinaki Area of the former Kuni Village.

A World FirstA World First

Neutralization Plantof Kusatsu

Through the neutralization project the Agatsuma River became so clean that fish now live there.

The long period of suffering caused by the damage created by the acidic waters seems like a distant memory.

To preserve this abundant environment, the Shinaki Dam Water Quality Management Office continues

to carry out the neutralization project 24/7.

Through the neutralization project the Agatsuma River became so clean that fish now live there.

The long period of suffering caused by the damage created by the acidic waters seems like a distant memory.

To preserve this abundant environment, the Shinaki Dam Water Quality Management Office continues

to carry out the neutralization project 24/7.

The resulting limewater is returned to the river to neutralize it

Limestone is stored in large silos at the Neutralization Plant

Limestone mining Limestone powder is mixed with acidic water drawn from the river

Water containinglimestone powder

River water

Limestonepowder Limestone powder granules are

0.075 mm in size.